1. Field of the Invention
This invention relates to a rotor for rotating an output shaft of a motor and a molding die for molding the rotor to manufacture the rotor.
2. Description of the Related Art
A stepping motor has been used as an actuator in various office automation equipment, domestic electrical equipment or an automobile. For example, in a vehicle, a meter for a vehicle to indicate a measured value, such as vehicle speed or engine speed, is mounted. In the meter for a vehicle, a stepping motor is applied to drive a pointer disposed in front of a dial plate.
Such type of stepping motors have a meter body mounted on a printed circuit board in the meter and a output shaft projecting from the meter body to mount the pointer thereon. The meter body includes a case, a stator fixed in the case and a rotor 100 shown in FIG. 11. The case is formed into a thin flat box shape. The stator has a frame fixed in the case and a coil mounted on the frame.
The rotor 100, as shown in FIG. 11, includes a disc-shape rotor body 101 and an annular-shape magnet 102 disposed coaxially with the rotor body 101. The rotor body may be made of synthetic resin. The magnet 102 is fixed on the rotor body 101 so as to expose an outer surface 102a thereof.
The rotor 100 is formed by means of inserting the magnet 102 into a cavity of the molding die and injecting fluidized synthetic resin by heating with high pressure into the cavity. Thus, the rotor 100 is formed with injection molding. The rotor body, i.e. the rotor, is supported freely rotatably by the case. When the rotor body, i.e. the rotor, rotates, the output shaft rotates.
When current flows through the coil of the stepping motor structured as mentioned above, the frame is magnetized to generate a rotating magnetic field and the rotor 100 is rotated. Then, the output shaft is rated and a pointer is moved.